she'll introduce senator john kerry tapped to take her place at his confirmation hearing. yesterday clinton spent more than 5 1/2 hours testifying before congress about the siege of the u.s. consulate in libya. she faced tough aggressive questions about the attacks which left four americans dead. margaret brennan reports. >> as i have said many times, i take responsibility. >> reporter: in her opening statement, the usually reserved hillary clinton said that for her the benghazi tragedy is personal. >> i stood next to president obama as the marines carried those flag draped caskets off the plane at andrews. i put my arms around the mothers and fathers, sisters and brothers, sons and daughter, and the wives left alone to raise their children. >> reporter: secretary clinton said that while she had a close relationship with ambassador chris stevens, his request for additional security never made it to her desk. >> the specific security requests pertaining to benghazi, you know, were handled by the security professionals in the department. i didn't see those requests. they did